For decades scientists have warned of a potential repeat of the 1918 flu pandemic, which claimed tens of millions of lives. The avian (H5N1) influenza virus drew the most attention. A decade ago, it killed tens of millions of birds, and any person who contracted the virus faced grim odds—the mortality rate is about 60 percent. Fortunately, the H5N1 virus did not spread in the air and thus could not infect humans easily, and outbreaks remained confined to small areas.

In 2011 two research groups independently discovered the genetic mutations necessary to make the H5N1 virus airborne and therefore more easily transmissible. They showed that ferrets infected with the mutant strains could transmit the virus to healthy ferrets caged nearby.

Concerns that bioterrorists could use the data to weaponize the virus led government officials, scientists and journal editors to hold off publishing the mutation information. Proponents argued that the data would help epidemiologists know what to watch out for if H5N1 mutated in the wild and better enable them to prepare countermeasures. That argument, plus the fact that many scientists had already obtained access to the information, led the U.S. National Science Advisory Board for Biosecurity to green-light the publications of the papers. The first appeared in the June 21 issue of Nature. —Philip Yam